Heart valves harvested from animals, such as porcine heart valves, have proven to be useable as bioprosthetic replacements for malfunctioning endogenous heart valve. These animal heart valves typically contain large amounts of connective tissue proteins, such as collagen and elastin. After the heart valve and/or other desired tissues have been harvested from the donor animals, they undergo a chemical "tanning" process wherein the connective tissue proteins within the tissue are exposed to one or more chemical cross linking agents (i.e., "fixatives" or "tanning agents") These crosslinking agents then react with the connective tissue proteins to form chemical cross linkages between (or sometimes within) the connective tissue protein molecules. The types of chemical cross linking agents useable for the tanning process include: formaldehyde, glutaraldehyde, dialdehyde starch, hexamethylene diisocyanate and certain polyepoxy compounds. The tanning process renders the animal tissue relatively inert with respect to the living host environment, and brings about fixation (i.e., stabilization) of the tissue so that it has a fixed configuration and does not degrade following implantation.
One particular type of bioprosthetic heart valve which has gained popularity among surgeons in recent years, is known as a "stentless aortic bioprosthesis." Such stentless aortic bioprostheses do not include any man-made stent or support frame, and are formed entirely of a preserved segment of the donor animal's aorta, having the aortic valve leaflets therein.
Examples of commercially available stentless bioprosthetic valves include the Edwards Prima.TM. Stentless Bioprosthesis (Baxter Edwards AG, Spierstrasse 5, CH-6848 Horw, Switzerland), the Medtronic Freestyle.TM. Aortic Root Bioprosthesis (Medtronic, Inc. 7000 Central Avenue NE, Minneapolis, Minn. 55432-3576) and the St. Jude Toronto.TM. SPV Stentless Bioprosthesis (St. Jude Medical, Inc. One Lillehei Plaza, St. Paul, Minn. 55117).
The tanning of stentless bioprosthetic heart valves presents unique technical challenges because, due to the absence of any stent or man made support structure, it is necessary to temporarily support the stentless bioprosthesis during its exposure to the tanning agent(s). A particular system and method for tanning of stentless bioprostheses has been described in U.S. Pat. No. 4,372,743 (Lane) entitled "Low-Pressure Fixation of Valvular Tissue Intended for Implantation." However certain components of this system are less than optimal for the tanning of some types of aortic bioprostheses. In particular, the fixation apparatus disclosed in U.S. Pat. No. 4,372,743 (Lane) does not fully support the Sinuses of Valsalva, located within the aortic portion of the bioprosthesis, and thus some deformation or collapse of these sinuses may occur during the tanning process.
Thus, there exists a need in the art for the development of a new system, apparatus and method for tanning of stentless aortic bioprostheses such that the Sinuses of Valsalva will be fixed in substantially open, non-collapsed configurations.